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M16
, M16A4]] The M16 rifle, officially designated Rifle, Caliber 5.56mm, M16 is the United States military version of the AR-15 rifle. The rifle was adapted for semi-automatic, three-round burst, and full-automatic fire. Colt purchased the rights to the AR-15 from ArmaLite, and currently uses that designation only for semi-automatic versions of the rifle. The M16 fires the 5.56x45mm NATO cartridge. The rifle entered US Army service and was deployed for jungle warfare operations in South Vietnam in 1963, becoming the US military's standard service rifle of the Vietnam War by 1969, replacing the M14 rifle in that role. The US Army retained the M14 in CONUS, Europe, and South Korea until 1970. Since the Vietnam War, the M16 rifle family has been the primary service rifle of the US Armed Forces. The M16 has also been widely adopted by other militaries around the world. Total worldwide production of M16s has been approximately 8 million, making it the most produced form of firearm of its caliber. In 2010, the M16 began to be phased out in the US Army and is being supplemented by the M4 carbine, which is itself a shortened derivative of the M16A2. __FORCETOC__ Introduction The M16 is a lightweight, 5.56mm, air-cooled, gas operated, magazine-fed assault rifle with a rotating bolt, actuated by direct impingement gas operation. The rifle is made of steel, 7075 aluminum alloy, composite plastics and polymer materials. The M16A4 rifle was standard issue for the USMC in Operation Iraqi Freedom after 2004; it replaced the M16A2 in front line units. In the US Army, the M16A2 rifle is being supplemented with two rifle models, the M16A4 and the M4 carbine, as the standard issue assault rifle. The M16A4 has a flat-top receiver developed for the M4 carbine, a handguard with four Picatinny rails for mounting a sight, laser, night vision device, forward handgrip, removable handle, or a flashlight. The M16 rifle is principally manufactured by Colt and Fabrique Nationale de Herstal, with variants made elsewhere in the world. Versions for the US military have also been made by H&R Firearms and most recently by Sabre Defense. Semi-auto versions of the AR-15 are popular recreational shooting rifles, with versions manufactured by other small and large manufacturers in the US. 5.56mm cartridge The 5.56x45mm cartridge originally developed by ArmaLite had many advantages over the 7.62x51mm NATO round used in the M14 Rifle. Most of these reasons were due to the dense and humid jungle in which US soldiers were fighting during the Vietnam War. The 5.56mm cartridge was developed as a more medium range alternative to the larger caliber round used in the M14 and M1A rifles; each soldier can carry more ammunition and engage enemy targets more effectively at shorter distances. It was also found useful in automatic and burst fire, developing the M16 into variants such as the M16A3 and current M16A4. History Summary ArmaLite sold its rights to the AR-15 to Colt in 1959. The AR-15 was first adopted in 1962 by the US Air Force, ultimately receiving the designation M16. The US Army began to field the XM16E1 en masse in 1965 with most of them going to the Republic of Vietnam, and the newly organized and experimental Airmobile Divisions. The USMC in South Vietnam also experimented with the M16 rifle in combat during this period. The XM16E1 was standardized as the M16A1 in 1967. This verison remained the primary infantry rifle of US forces in South Vietnam until the end of the war in 1973, and remained with all US military ground forces after it had replaced the M14 service rifle in 1970 in CONUS, Europe (Germany), and South Korea; when it was supplemented with the M16A2. During the early 1980s a roughly standardized load for this ammunition was adopted throughout NATO. The M16A3 is a fully automatic variant of the M16A2, issued within the US Navy. The M16A2 is currently being supplemented by the M16A4, which incorporates the flattop receiver unit developed for the M4 carbine, and a Picatinny rail system. M16A2s are still in stock with the US Army and Marine Corps, but are used primarily by reserve and National Guard units as well as by the US Air Force. The first issues of the rifle generated considerable controversy because the gun suffered from a jamming flaw known as "failure to extract", which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out the muzzle. According to a congressional report, the jamming was caused primarily by a change in gunpowder that was done without adequate testing and reflected a decision for which the safety of soldiers was a secondary consideration. Due to this issue, reports of soldiers being wounded were directly linked to the M16, which many soldiers felt was unreliable compared to its precusor, the M14. Project SALVO In 1948, the US Army organized the civilian Operations Research Office, mirroring similar operations research organizations in the UK. One of their first efforts, Project ALCLAD, studied body armor and the conclusion was that they would need to know more about battlefield injuries in order to make reasonable suggestions. Over 3 million battlefield reports from WWI and WWII were analyzed and over the next few years they released a series of reports on their findings. The conclusion was that most combat takes place at short range. In a highly mobile war, combat teams ran into each other largely by surprise; and the team with the higher firepower tended to win. They also found that the chance of being hit in combat was essentially random; accurate "aiming" made little difference because the targets no longer sat still. The number one predictor of casualties was the total number of bullets fired. Other studies of behavior revealed that many US infantrymen (as many as two-thirds) never actually fired their rifle in combat. By contrast, soldiers armed with rapid fire weapons were much more likely to have fired their weapons in battle. These conclusions suggested that infantry should be equipped with a fully automatic rifle of some sort in order to increase the actual firepower of regular soldiers. It was also clear, however, that such weapons dramatically increased ammunition use and in order for a rifleman to be able to carry enough ammunition for a firefight he would have to carry something much lighter. Existing rifles met none of these criteria. Although it appeared the new 7.62mm T44 (precursor to the M14) would increase the rate of fire, its heavy 7.62mm NATO cartridge made carrying significant quantities of ammunition difficult. Moreover, the length and width of the weapon made it unsuitable for short range combat situations often found in jungle and urban combat of mechanized warfare, where a smaller and lighter weapon could be brought to bear faster. These efforts were noticed by Colonel Rene Studler, US Army Ordnance's Chief of Small Arms Research and Development. Col. Studler asked the Aberdeen Proving Ground to submit a report on the smaller caliber weapons. A team led by Donald Hall, director of program at Aberdeen, reported that a .22 inch (5.56mm) round fired at a higher velocity would have performance equal to larger rounds in most combat. With the higher rate of fire possible due to lower recoil it was likely that such a weapon would inflict more casualties on the enemy. His team members started development of a series of experimental .22 cartridges. In 1955, their request for further funding was denied. A new study, Project SALVO, was set up to try to find a weapon design suited to real-world combat. Running between 1953 and 1957 in two phases, SALVO eventually suggested that a weapon firing four rounds into a 20 inch area would double the hit probability of existing semi-automatic weapons. In the second phase, SALVO II, several experimental weapons concepts were tested. Irwin Barr of AAI Corporation introduced a series of flechette weapons, starting with a shotgun shell containing 32 darts and ending with single-shot flechette "rifles". Winchester and Springfield Armory offered multiple barrel weapons, while ORO's own design used two .22, .25, or .27 caliber bullets loaded into a single .308 Winchester or .30-06 cartridge. Eugene Stoner Meanwhile testing of the 7.62mm T44 continued, and Fabrique Nationale also submitted their new FN FAL via the American firm Harrington & Richardson as the T48. The T44 was selected as the new battle rifle of the US Army despite a strong showing by the T48. In 1954, Eugene Stoner of the newly formed ArmaLite helped develop the 7.62mm AR-10. Springfield's T44 and similar entries were conventional rifles using wood for the "furniture" and otherwise built entirely of steel using mostly forged and machined parts. ArmaLite was founded specifically to bring the latest in designs and alloys to firearms design, and Stoner felt he could easily beat the other offerings. The AR-10's receiver was made of forged and milled aluminum alloy instead of steel. The barrel was mated to the receiver by a separate hardened steel extension to which the bolt locked. This allowed a lightweight aluminum receiver to be used while still maintaining a steel-on-steel lockup. The bolt was operated by high-pressure combustion gases taken from a hole in the middle of the barrel directly through a tube above the barrel to a cylinder created in the bolt carrier with the bolt carrier itself acting as a piston. Traditional rifles located this cylinder close to the gas vent. The stock and grips were made of a glass-reinforced plastoc shell over a rigid foam plastic core. The muzzle brake was fabricated from titanium. Over Stoner's objections, various experimental composite and 'Sullaloy' aluminum barrels were fitted to some AR-10 prototypes by ArmaLite's president, George Sullivan. The Sullaloy barrel was made entirely of heat-treated aluminum, while the composite barrels used aluminum extruded over a thin stainless steel liner. Meanwhile, the layout of the weapon itself was also somewhat different. Previous designs generally placed the sights directly on the barrel, using a bend in the stock to align the sights at eye level while transferring the recoil down to the shoulder. This meant that the weapon tended to rise when fired, making it very difficult to control during automatic fire. The ArmaLite team used a solution previously used on weapons such as the German FG42 and Johnson light machinegun; they located the barrel in line with the stock, well below eye level, and raised the sights to eye level. The rear sight was built into a carrying handle over the receiver. Despite beign over 2 lb lighter than the competition, the AR-10 offered significantly greater accuracy and recoil control. Two prototype rifles were delivered to the US Army's Springfield Armory for testing in late 1956. At the time, the US Armed forces were already two years into a service rifle evaluation program, and the AR-10 was a newcomer with respect to older, more fully developed designs. Over Stoner's continued objections, George Sullivan had insisted that both prototypes be fitted with composite aluminum/steel barrels. Shortly after a composite barrel burst on one prototype in 1957, the AR-10 was rejected. The AR-10 was later produced by a Dutch firm, Artillerie Inrichtingen, and saw limited but successful military service with several foreign nations such as Sudan, Guatemala, and Portugal. Portugal deployed a number of AR-10s for use by its airborne battalions, and the rifles saw considerable combat service in Portugal's counter-insurgency campaigns in Angola and Mozambique. Some AR-10 rifles were still in service with airborne forces serving during the withdrawal from Portugese Timor in 1975. CONARC In 1957, a copy of Gustafson's funding request from 1955 found its way into the hands of General Willard G. Wyman, commander of the US Continental Army Command. He immediately put together a team to develop a .223 caliber weapon for testing. Their finalized request called for a select-fire weapon of 6 lbs when loaded with 20 rounds of ammunition. The bullet had to penetrate a standard US steel helmet, body armor, or a steel plate of 0.135 in and retain a velocity in excess of the speed of sound at 500 yds, while equaling or exceeding the "wounding" ability of the .30 Carbine. Wyman had seen the AR-10 in an earlier demonstration, and impressed by its performance he personally suggested that ArmaLite enter a weapon for testing using a 5.56mm cartridge designed by Winchester. Their first design, using conventional layout and wooden furniture, proved to be too light. When combined with a conventional stock, recoil was excessive in fully automatic fire. Their second design was simply a scaled-down AR-10, and immediately proved much more controllable. Winchester entered the LMR, a design based loosely on their M1 Carbine, and Earle Harvey of Springfield attempted to enter a design, but was overruled by his superiors at Springfield, who refused to divert resources from the T44. In the end, ArmaLite's AR-15 had no competition. The lighter round allowed the rifle to be scaled down, and was smaller and lighter than the previous AR-10. The AR-15 weighed only about 5.5 lb empty, and 6 lbs loaded (with a 20-round magazine). During testing in March 1958, rainwater caused the barrels of both the ArmaLite and Winchester rifles to burst, causing the Army to once again press for a larger round, this time at 0.258 in (6.6mm). Nevertheless, they suggested continued testing for cold-weather suitability in Alaska. Stoner was later asked to fly in to replace several parts, and when he arrived he found the rifles had been improperly reassembled. When he returned he was surprised to learn that they too had rejected the design even before he had arrived; their report also endorsed the 0.258 in round. After reading these reports, General Maxwell Taylor became dead-set against the design, and pressed for continued production of the M14. Not all the reports were negative. In a series of mock-combat situations testing the AR-15, M14, and AK-47, the Army found that the AR-15's small size and light weight allowed it to be brought to bear much more quickly, just as CONARC had suggested. Their final conclusion was that an 8-man team equipped with the AR-15 would have the same firepower as a current 11-man team armed with the M14. US troops were able to carry more than twice as much 5.56x45mm ammunition as 7.62x51mm NATO for the same weight, which would allow them a greater advantage against a typical NVA unit armed with AK-47s. At this point, Fairchild had spent $1.45 million in development expenses, and wished to divest itself of its small-arms business. Fairchild sold production rights for the AR-15 to Colt Firearms in December 1959, for only $75,000 in cash and a 4.5% royalty on subsequent sales; Robert W. MacDonald of Cooper-MacDonald got a finder's fee of $250,000 and a 1% royalty for arranging the deal. In 1960, ArmaLite was reorganized and Stoner left the company. M16 adoption Curtis LeMay viewed a demonstration of the AR-15 in July 1960. In the summer of 1961, General LeMay had been promoted to the position of USAF Chief of Staff and requested an order of 80,000 AR-15's for the US Air Force. However, under the recommendation of General Maxwell D. Taylor, who advised the Commander in Chief that having two calibers within the military system at the same time would be problematic, President Kennedy turned down the request. However, Advanced Research Projects Agency, which had been created in 1958 in response to the Soviet Sputnik program, embarked on project AGILE in the spring of 1961. AGILE's priority mission was to devise inventive fixes to the communist problem in South Vietnam. In October 1961, William Godel, a senior man at ARPA, sent 10 AR-15s to South Vietnam to let the allies test them. The reception was enthusiastic, and in 1962 another 1,000 AR-15s were sent to South Vietnam. Special Operations units and advisers working with the South Vietnamese troops filed battlefield reports lavishly praising the AR-15 and the stopping effectiveness of the 5.56mm cartridge, and pressed for its adoption. However, what no one knew, except the men directly using the AR-15 in Vietnam, were the devastating kills made by the new rifle, photographs of which, showing enemy casualties made by the .223 (5.56mm) bullet remained classified into the 1980s. The damage caused by the .223 "varmint" bullet was observed and originally thought to be caused by "tumbling" due to the slow 1 in 14-inch rifling twist rate. However, this twist rate only made the bullet less stable in the air. The large wounds observed by soldiers in Vietnam were acutally caused by projectile fragmentation, which was created by a combination of the projectile's velocity and construction. US Secretary of Defense Robert McNamara now had two conflicting views: the ARPA report favoring the AR-15 and the Pentagon's position on the M14. Even President John F. Kennedy expressed concern, so McNamara ordered Secretary of the Army Cyrus Vance to test the M14, the AR-15, and the AK-47. The Army's test report stated that only the M14 was suitable for Army use, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used; the Inspector General confirmed that the testers showed favor to the M14. Secretary Robert McNamara ordered a halt to M14 production in January 1963, after receiving reports that M14 production was insufficient to meet the needs of the armed forces. Secretary McNamara had long been a proponent of weapons program consolidation among the armed services. At the time, the AR-15 was the only rifle that could fulfill a requirement of a "universal" infantry weapon for issue to all services. McNamara ordered the weapon be adopted unmodified, in its current configuration, for immediate issue to all services, despite receiving reports noting several deficiencies with the M16 as a service rifle, including the lack of a chrome-lined bore and chamber, the 5.56mm projectile's instability under arctic conditions, and the fact that large quantities of 5.56mm ammunition required for immediate service were not available. In addition, the Army insisted on the inclusion of a foward assist to help push the bolt into battery in the event that a cartridge failed to seat in the chamber through fouling or corrosion. Colt had argued the rifle was a self-cleaning design, requiring little or no maintenance. Colt, Eugene Stoner, and the US Air Force believed that a forward assist needlessly complicated the rifle, adding about $4.50 to its procurement cost with no real benefit. As a result, the design was split into two variants: the Air Force's M16 without the forward assist, and, for the other service branches, the XM16E1 with the forward assist. In November 1963, McNamara approved the US Army's order of 85,000 XM16E1s for jungle warfare operations; and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s. Meanwhile, the Army carried out another project, the Small Arms Weapons Systems, on general infantry firearm needs in the immediate future. They recommeded the immediate adoption of the weapon. Later that year the Air Force officially accepted their first batch as the United States Rifle, Caliber 5.56mm, M16. The Army immediately began to issue the XM16E1 to infantry units. However, the rifle was initially delivered without adequate cleaning supplies or instructions and so, when the M16 reached Vietnam with US troops in March 1965, reports of stoppages in combat began to surface. Often the gun suffered from a stoppage known as "failure to extract", which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out of the muzzle. Although the M14 featured a chrome-lined barrel and chamber to resist corrosion in combat conditions, neither the bore nor the chamber of the M16/XM16E1 was chrome-lined. Several documented accounts of troops killed by enemy fire with inoperable rifles broken-down for cleaning eventually brought a Congressional investigation. :: We left with 72 men in our platoon and came back with 19. Believe it or not, you know what killed most of us? Our own rifle. Practically every one of our dead was found with his M16 torn down next to him where he had been trying to fix it. ::: - Marine Corps Rifleman, Vietnam The root cause of the stoppages turned out to be a problem with the powder for the ammunition. In 1964, when the Army was informed that DuPont could not mass-produce the nitrocellulose-based powder to the specifications demanded by the M16, the Olin Mathieson Company provided a high-performance ball propellant of nitrocellulose and nitroglycerin. While the Olin WC 846 powder was capable of firing an M16 5.56mm round at the required 3,300 ft/s, it had the unintended consequence of increasing the rate of fire from 850 to 1,000 rounds per minute. This would leave behind dirty residue, making the M16 more likely to have a stoppage. The problem was resolved by fitting the M16 with a buffer system, slowing the rate of fire back down to 850 rpm and outfitting all newly produced M16s with an anti corrosive chrome-plated chamber. On 28 Feb, 1967, the XM16E1 was standardized as the M16A1. Major revisions to the design followed. The rifle was given a chrome-lined chamber (and later, the entire bore) to eliminate corrosion and stuck cartridges, and the rifle's recoil mechanism was re-designed to acommodate Army-issued 5.56mm ammunition. Rifle cleaning tools and powder solvents/lubricants were issued. Intensive training programs in weapons cleaning were instituted, and a comic book style manual was circulated among the troops to demonstrate proper maintenance. The reliability problems of the M16 diminished quickly, although the rifle's reputation continued to suffer. According to a Feb 1968 Department of Defense report the M16 rifle achieved widespread acceptance by US troops in Vietnam. Only 38 of 2,100 individuals queried wanted to replace the M16 with another weapon. Of those 38, 35 wanted the CAR-15 (a shorter version of the M16) instead. NATO standards In March 1970, the US stated that all NATO forces should eventually adopt the 5.56x45mm NATO cartridge. This shift represented a change in the philosophy of the military's long-held position about caliber size. By the mid-1970s, other armies were also looking at M16-style weapons. A NATO standardization effort soon started, and tests of various rounds were carried out starting in 1977. The US offered their original 5.56x45mm design, the M193, with no modifications, but there were concerns about its penetration in the face of the wider introduction of body armor. In the end, the Belgian 5.56x45mm SS109 round was chosen (STANAG 4172). This round was based on the US cartridge, but included a new 62 grain bullet design with a small steel tip added to improve penetration. The US Marine Corps was first to adopt the round with the M16A2, introduced in 1982. This was to become the standard US military rifle. The NATO 5.56x45mm standard ammunition produced for US forces is designated M855. Shortly after, in October 1980, NATO accepted the 5.56x45mm NATO cartridge. Draft Standardization Agreement 4179 was proposed to allow the military services of member nations to easily share rifle ammunition and magazines during operations, at the individual soldier level, in the interest of easing logisitical concerns. The magazine chosen to become the STANAG magazine was originally designed for the M16 rifle. Many NATO members, but not all, developed or purchased rifles with the ability to accept this type of magazine. However, the standard was never ratified and remains a 'Draft STANAG'. The NATO Accessory Rail STANAG 4694, or Picatinny rail STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles to provide a standardized mounting platform. The rail comprises of a series of ridges with a T-shaped cross section interspersed with flat "spacing slots". Scopes are mounted either by sliding them on from one end or the other; by means of a "rail-grabber" which is clamped to the rail with bolts, thumbscrews or levers; or onto the slots between the raised sections. The rail was originally for scopes. However, once estabilished, the use of the system was expanded to other accessories, such as tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets. Currently, te M16 is in use by 15 NATO countries and more than 80 worldwide. Extended Magazines In addition to Colt's straight 20-round magazine, a proprietary fully curved 30-round magazine (like the AK-47) was also commercially available from 1964. However, it didn't work with all models of the rifles (or even some individual rifles) because the magazine well was designed to work with straight magaxines and the weapon either would or wouldn't feed reliabily when it used the extended magazine. When Special Forces personnel in Vietnam were trained on use of the XM177 Colt Commando assault-carbine in 1966, the few 30-round magazines used duirng the demonstrations were very popular. A request was made to have the XM177 "Commando" weapon ship with extended magazines if they could be made more reliable. Colt was too busy working on other technical issues of the AR-15 and XM177 to rework the extended magazines. Special Operations forces like the Rangers, Special Forces, and SEALs tried to scrounge as many of the extended magazines as they could in-theater. The US Air Force, who had procured a small supply of the extended magazine for use by their Military Police and Air Commandos, had to secure them from being requisitioned by the other services. An improved slightly curved 30-round magazine was finally developed by Colt in 1968 to meet a Special Operations requirement and began issue in 1969. It was mostly used by Special Operations forces, but began filtering through to regular units in the field. The improved extended magazine was adopted as Vietnam issue in 1970 when the M16A1 replaced the M14 as the military's standard service rifle. The improved extended 30-round magazine became military standard issue in 1975 and the original 20-round magazine became obsolete. An experimental 50-round magazine was designed in 1969 by Naval Weapons Laboratory Dahlgren and was machined at Naval Ordnace Station Forest Park to meet a 1968 Navy SEALs requirement for an extended magazine. The prototype was made from welding several 20-round magazines together and used a longer and heavier magazine spring. This design had two problems. If a strong magazine spring was used, the magazine fed reliably but it was too strong to load it completely without a loading tool and the bottom rounds might jam. If a weaker magazine spring was used, it could be reloaded by hand but failed to feed smoothly, completely, or even at all. The Mark 1 prototype was made from welding a 20-round magazine to an improved 30-round magazine. it used two constant tension magazine springs that attached to the top of the magazine to pull the follower up rather than push it and used a low-friction plastic follower rather than the aluminmum one - which allowed easy loading, steady feeding, and reduced jams. The later Mark 2 was similar but was fabricated like a regular magazine and had a sharper curve at the joint than the Mark 1 to allow more reliable feeding. The Mark 3 model incorporated improvements - one was a bolt hold-open device to indicate when the magazine was empty. SEAL Team 2 operators testing the Mark 3 model in the field found the magazine could only feed 45 rounds reliably (compared to 18 rounds for the short magazine and 28 for the extended magazine) adn the longer magazine made it difficult to fire from a prone position. The sustained firepower the magazine provided made up for these faults and a proposal was made in 1971 to issue at least one to every SEAL operative. As the Vietnam War began winding down, budget cuts forced the Navy to shelf the program in 1971 and no further magazines were made. Additional firepower All current M16 type rifles are designed to fire STANAG (NATO standard) 22mm rifle grenades from their integral flash hiders without the use of an adapter. These 22mm grenade types range from powerful anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. The US military does not generally use rifle greandes; however, they are used by other nations. All current M16 type rifles can mount under-barrel 40mm grenade launchers, such as the M203 and M320. Both use the same 40mm grenades as the older, stand-alone M79 Grenade Launcher. The M16 can also mount under-barrel 12 gauge shotguns such as the KAC Masterkey or the M26 Modular Accessory Shotgun System. Riot Control Launcher The M234 Riot Control Launcher is an M16 series rifle attachment firing a M755 blank round. The M234 mounts on the muzzle, bayonet lug, and front sight post of an M16. It fires either the M734 64mm Kinetic Riot Control or the M724 64mm CSI Riot Control Ring Airfoil Projectiles. The latter produces a 4 to 5 foot Tear Gas cloud on impact. The main advantage of using a Ring Airfoil Projectiles is that their design does not allow them to be thrown back by rioters with any real effect. The M234 is no longer used by US forces. It has been replaced by the M203 grenade launcher and nonlethal ammunition. Design .]]The M16's receivers are made of 7075 aluminum alloy, its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics. Early models were especially lightweight at 6.5 lbs without magazine and sling. This was significantly less than older 7.62mm "battle rifles" of the 1950s and 1960s. It also compares with the 6.5 lbs AKM without magazine. The M16A2 and later variants weigh more because of the adoption of a thicker barrel profile. The thicker barrel is more resistant to damage when handled roughly and is also slower to overheat during sustained fire. Unlike a traditional "bull" barrel that is thick its entire length, the M16A2's barrel is only thick forward of the handguards. The barrel profile under the handguards remained the same as the M16A1 for compatibility with the M203 grenade launcher. The rifle is the same length as the M16A2. The rifling twist of early model M16 barrels had 4 grooves, right hand twist, 1 turn in 14 inches bore-as it was the same rifling used by the .222 Remington Sporting round. This was shown to make the light .223 Remington bullet yaw in flight at long ranges and it was soon replaced. Later models had an improved rifling with 6 grooves, right hand twist, 1 turn in 12 inches for increased accuracy and was optimized for use with the standard US M193 cartridge. Current models are optimized for the heavier NATO SS109 bullet and have 6 grooves, right hand twist, 1 turn in 7 in. Weapons designed to accept both the M193 or SS109 rounds have a 6 groove, right hand twist, 1 turn in 9 inches bore. The M16's most distinctive ergonomic feature is the carrying handle and rear sight assembly on top of the receiver. This is a byproduct of the original design, where the carry handle served to protect the charging handle. As the line of sight is 2.5 in over the bore, the M16 has an inherent parallax problem. At closer ranges, the shooter must aim high in order to place the shots where desired. The M16 has a 500mm sight radius. It uses an L-type flip, aperture rear sight, and is adjustable with two settings, 0-300m and 300-400m. The front sight is post adjustable for elevation in the field. The rear sight can be adjusted in the field for windage. The sights can be adjusted with a bullet tip and soldiers are trained to zero their own rifles. The sight picture is the same as the M14, M1 Garand, M1 Carbine, and the M1917 Enfield. The M16 also has a "Low Light Level Sight System", which includes a front sight post with a small glass vial of (glow-in-the-dark) radioactive Tritium H3 and a larger aperture rear sight. The M16 can mount a scope on the carrying handle. With the advent of the M16A2, a new fully adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800m and to allow windage adjustments without the need of a tool or cartridge. Modern versions of the M16 use a Picatinny rail, which allows the use of various scopes and sighting devices. The current US Army and Air Force issue M4 Carbine comes with the M68 Close Combat Optic and Back-up Iron Sight. The US Marine Corps uses the ACOG Rifle Combat Optic and the US Navy uses EOTech Holographic Weapon Sight. Another ergonomic feature is its straight-line recoil design, where the recoil spring is located in the stock directly behind the action. This serves the dual function of operating spring and recoil buffer. The stock being in line with the bore reduces muzzle rise, especially during automatic fire. Because recoil does not significantly shift the point of aim, faster follow up shots are possible and user fatigue is reduced. The M16 utilizes direct impingement gas operation; energy from high-pressure gas tapped from a non-adjustable port built into the front sight assembly actuates the moving parts in the weapon. Combustion gases travel via a gas tube above the barrel directly into a chamber in the bolt carrier behind the bolt itself, pushing the carrier away from the bolt. This reduces the number of moving parts by eliminating the need for a separate piston and cylinder and it provides better performance in rapid fire by keeping reciprocating masses on the same axis as the bore. The M16 rifle fires the 5.56x45mm NATO cartridge and can produce massive wounding effects when the bullet impacts at high velocity and yaws in tissue leading to fragmentation and rapid transfer of energy. This produces wounds that were so devastating that the International Committee of the Red Cross and many countries considered the M16 to be an inhumane weapon. Variants Pre-Production ArmaLite AR-15 The weapon that eventually became the M16 series only had a vague resemblance to its offspring. The rifle was basically a scaled-down AR-10 with an ambidextrious charging handle located within the carrying handle, a narrower front sight "A" frame and no flash suppressor AR-15 (Colt Models 601 & 602) Colt's first two models produced after the acquisition of the rifle from ArmaLite were the 601 and 602, and these rifles were in many ways clones of the original ArmaLite rifle. The 601 and 602 are clearly identified by their flat lower receivers without raised surfaces around the magazine well and occasionally green or brown furniture. The 601 was adopted first of any of the rifles by the USAF and was quickly supplemented with the XM16 (Colt Model 602) and later the M16 as improvements were made. There was also a limited purchase of 602s, and a number of both of these rifles found their way to a number of special operations unis then operating in SE Asia. The only major difference between the 601 and the 602 is the switch from the original 1:14 inch rifling twist to the more common 1:12 in twist. These weapons were equipped with a triangular charging handle and a bolt hold open device that lacked a raised lower engagement surface. The bolt hold open device had a slanted and serrated surface that had to be engaged with a bare thumb, index finger, or thumb nail because of the lack of this surface. The USAF continued to use the AR-15 marked rifles in various configurations into the 1990s. M16 Variant originally adopted by the US Air Force. This was the first M16 adopted operationally. This variant had triangular handguards, butt stocks without a compartment for the storage of a cleaning kit, a three-pronged flash suppressor, and no forward assist. Bolt carriers were originally chrome plated and slick-sided, lacking forward assist notches. Later, the chrome plated carriers were dropped in favor of Army issued notched and parkerized carriers thought the interior portion of the bolt carrier is still chrome lined. The Air Force continued to operate these weapons until around 2001, at which time the Air Force converted all of its M16s to the M16A2 configuration. The M16 was also adopted by the British SAS, who used it during the Falklands War. XM16E1 and M16A1 (Colt Model 603) The US Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the bolt carrier. The M16A1 was the finalized production model in 1967. To address issues raised by the XM16E1's testing cycle, a closed, bird-cage flash suppressor replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves. Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued, while barrels with chrome-lined chambers and later fully lined bores were introduced. The front sight was now a square posed with 4 detent positions, adjustable for vertical zeroing by using a cartridge, nail, or special tool. With these and other changes, the malfunction rate slowly declined and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button whil closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from being inavertedly pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such as way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject unless corrected. The M16A1 is no longer in service with the US, but is still standard issue in many world armies. M16A2 The development of the M16A2 rifle was originally requested by the United States Marine Corps as a result of the USMC's combat experience in Vietnam with the XM16E1 and M16A1. The Marines were the first branch of the US Armed Forces to adopt the M16A2 in the early/mid-1980s, with the US Army following suit in the late 1980s. Modifications to the M16A2 were extensive. In addition to the new rifling, the barrel was made with a greater thickness in front of the front sight post, to resist bending in the field and to allow a longer period of sustaine fire without overheating. The rest of the barrel was maintained at the original thickness to enable the M203 grenade launcher to be attached. A new adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800m to take full advantage of the ballistic characteristics of the new SS109 rounds and to allow windage adjustments without the need of a tool or cartridge. The flash suppressor was again modified, this time to be closed on the bottom so it would not kick up dirt or snow without the need of a tool or cartridge. The flash suppressor was again modified from the original triangular shape to a round one, which better fitted smaller hands and could be fitted to older models of the M16. The new handguards were also symmetrical so that armories need not separate left or right spares. The handguard retention ring was tapered to make it easier to install and uninstall the handguards. A notch for the middle finger was added to the pistol grip, as well as more texture to enhance the grip. The buttstock was lengthened by 5/8 in. The new buttstock became ten times stronger than the original due to advances in polymer technology since the early 1960s. Original M16 stocks were made from fiberglass-impregnated resin; the newer stocks were engineered from DuPont Zytel glass-filled thermoset polymers. The new stock included a fully textured polymer buttplate for better grip on the shoulder, and retained a panel for accessing a small compartment inside of the stock, often used for storing a basic cleaning kit. The A2 also uses a faster twist rifling to allow the use of a trajectory-matched tracer round. A spent case deflector was incorporated into the upper receiver immediately behind the ejection port to prevent cases from striking left-handed users. The action was also modified, replacing the fully automatic setting with a three-round burst setting. When using a fully automatic weapon, inexperienced troops often hold down the trigger and "spray" when under fire. The US Army concluded that three-shot groups provide an optimum combination of ammunition conservation, accuracy, and firepower. The USMC has retired the M16A2 in favor of the newer M16A4. However, many M16A2s remain in service in US Army, Air Force, and Coast Guard service. M16A3 The M16A3 is a fully automatic variant of the M16A2 adopted in small numbers around the time of the introduction of the M16A2, primarily by the US Navy for use by SEAL, Seabee, and security units. It features the M16A1 trigger group providing "safe", "semi-automatic", and "fully automatic" modes. M16A4 The M16A4 is the fourth generation of the M16 series. It is equipped with a removable carrying handle and full length quad Picatinny rail for mounting optics and other ancillary devices. The FN M16A4, using safe/semi/burst selective fire, is now the standard issue for all USMC and a few select US Army units, and is the current issue to Marine Corps' recruits in both MCRD San Diego and MCRD Parris Island. Military issue rifles are also equipped with a Knight's Armament Company M5 RAS hand guard, allowing vertical grips, lasers, tactical lights, and other accessories to be attached, coining the designation M16A4 MWS (or Modular Weapon System) in US Army field manuals. Colt also produces M16A4 models for international purchases, with specifics selective fire: *R0901 / NSN 1005-01-383-2872 (Safe/Semi/Auto) *R0905 (Safe/Semi/Burst) The Marine Corps is considering a Product Improvement Program (PIP) for their M16A4 MWS rifles. Potential features include a modular and adjustable stock, ambidextrious fire selector, heavier barrel, improved trigger, free-floating rail system and an adjustable gas block and gas regulator to give all rifles a suppression capability. Summary Derivatives XM177 : Main article: CAR-15 In Vietnam, some soldiers were issued a carbine version of the M16 called the XM177. The XM177 had a shorter 10 in barrel and a telescoping stock, which made it substantially more compact. It also possessed a combination flash hider/sound moderator to reduce problems with muzzle flash and loud report. The USAF's GAU-5/A (XM177) and the US Army's XM177E1 variants differed over the latter's inclusion of a forward assist, although some GAU-5s do have the forward assist. The final USAF GAU-5A/A and the US Army XM177E2 had an 11.5 in barrel with a longer flash/sound suppressor. The lengthening of the barrel was to support the attachment of Colt's own XM148 40mm grenade launcher. These versions were known as the Colt Commando model commonly referenced and marketed as the CAR-15. The variants were issued in limited numbers to special forces, helicopter crews, Air Force pilots, Air Force Security Police Military Working Dog (MWD) handlers, officers, radio operators, artillerymen, and troops other than frontline riflemen. Some USAF GAU-5A/As were later equipped with even longer 14.5 in barrels as the two shorter versions were worn out. These were effectively used by the British SAS during the Falklands War. Colt Model 733 Colt also returned to the original "Commando" idea, with its Model 733, essentially a modified XM177E2 with many of the features introduced on the M16A2. M231 Firing Port Weapon (FPW) The M231 Firing Port Weapon (FPW) is an adaped version of the M16 assault rifle for firing from ports on the M2 Bradley. The infantry's normal M16s are too long for use in a "buttoned up" APC, so the FPW was developed to provide a suitable weapon for this role. Designed by the Rock Island Arsenal, the M231 FPW remains in service, although all but the two rear firing ports on the Bradley have been removed. The M231 FPW is often used by dismounted Mechanized Infantry during trench clearing and urban warfare operations due to its compact size and high rate of fire. The M231 fires from the open bolt and is only configured for fully automatic fire. The open bolt configuration gives the M231 a much higher cyclic rate of fire than the closed bolt operation of the M16A1. Mk 4 Mod 0 The Mk4 Mod 0 was a variant of the M16A1 produced for the US Navy SEALs during the Vietnam War and adopted in April 1970. It differed from the basic M16A1 primarily in being optimized for marittime operations and coming equipped with a sound suppressor. Most of the operating parts of the rifle were coated in Kal-Guard, a hole of 0.25 in was drilled through the stock and buffer tube for drainage, and an O-ring was added to the end of the buffer assembly. The weapon could reportedly be taken to the depth of 200 ft in water without damage. The initial Mk 2 Mod 0 Blast Suppressor was based on the US Army's Human Engineering Labs (HEL) M4 noise suppressor. The HEL M4 vented gas directly from the action, requiring a modified bolt carrier. Thus, the HEL M4 suppressor was permanently mounted though it allowed normal semi-automatic and automatic operation. If the HEL M4 suppressor were removed, the weapon would have to be manually loaded after each single shot. On the other hand, the Mk 2 Mod 0 blast suppressor was considered an integral part of the Mk 4 Mod 0 rifle, but it would funciton normally if the suppressor were removed. The Mk 2 Mod 0 blast suppressor also drained water much more quickly and did not require any modification to the bolt carrier or to the charging handle. In the late 1970s, the Mk 2 Mod 0 blast suppressor was replaced by the Mk 2 blast suppressor made by Kight's Armament Company. The KAC suppressor can be fully submerged and water will drain out in less than 8 seconds. It will operate without degradation even if the rifle is fired at the maximum rate of fire. The US Army replaced the HEL M4 with the much simpler Studies in Operational Negation of Insurgency and Counter-Subversion (SIONICS) MAW-A1 noise and flash suppressor. Mark 12 Developed to increase the effective range of soldiers in the designated marksman role, the US Navy developed the Mark 12 Special Purpose Rifle (SPR). Configurations in service vary, but the core of the Mark 12 SPR is an 18" heavy barrel with muzzle brake and free float tube. This tube relieves pressure on the barrel caused by standard handguards and greatly increases the potential accuracy of the system. Also common are higher magnification optics ranging from the 6x power Trijicon ACOG to the Leupold Mark 4 Tactical rifle scopes. Firing Mark 262 Mod 0 ammunition with a 77gr Open tip Match bullet, the system has an official effective range of 600+ meters. However, published reports of confirmed kills beyond 800 m from Iraq and Afghanistan are not uncommon. M4 carbine : Main article: M4 carbine The M4 carbine was developed from various outgrowths of these designs, including a number of 14.5 in barreled A1 style carbines. The XM4 started its trials in the mid-1980s, with a barrel of 14.5 inches. Officially adopted as a replacement for the M3 "Grease Gun" (and the Beretta M9 and M16A2 for select troops) in 1994, it was used with great success in the Balkans and in more recent conflicts, including the Afghanistan and Iraq theaters. The M4 carbine has a three-round burst firing mode, while the M4A1 carbine has fully automatic firing mode. Both have a Picatinny rail on the upper receiver, allowing the carry handle/rear sight assembly to be replaced with other sighting devices. International derivatives C7 and C8 The Diemaco C7 and C8 are updated variants of the M16 developed and used by the Canadian Forces and are now manufactured by Colt Canada. The C7 is a further development of the experimental M16A1E1. Like earlier M16s, it can be fired in either single shot or automatic mode, instead of the burst function selected for the M16A2. The C7 also features the structural strengthening, improved handguards, and longer stock developed for the M16A2. Diemaco changed the trapdoor of the buttstock to make it easier to access and a spacer of 0.5 inches is available to adjust stock length to user preference. The most noticeable external differerences between American M16A2s and Diemaco C7s is the retention of the A1 sytle rear sights. Not easily apparent is Diemaco's use of hammer-forged barrels. The Canadians originally desired to use a heavy barrel profile instead. The C7 has been developed to the C7A1, with a Weaver rail on the upper receiver for a C79 optical sight, and to the C7A2, with different furniture and internal improvements. The Diemaco produced Weaver rail on the original C7A1 variants does not meet the M1913 Picatinny standard, leading to some problems with mounting commerical sights. This is easily remedied with minor modifications to the upper receiver or the sight itself. Since Diemaco's acquisition by Colt to form Colt Canada, all Canadian produced flattop upper receivers are machined to the M1913 standard. Others * The Chinese Norinco CQ is an unlicensed derivative of the M16A1 made specifically for export, with the most obvious differences being in its handguard and revolver-style pistol grip. *Terab rifle is the Norinco CQ manufactured by the MIC of Sudan. *The MSSR rifle developed as an effective, low cost sniper rifle by the Philippine Marine Corps Scout Snipers. *Taiwan uses piston-drived M16-based weapons as their standard rifle. These include the T65, T86, and T91 assault rifles. Production and Users The M16 is the most commonly manufactured 5.56x45mm rifle in the world. Currently, the M16 is in use by 15 NATO countries and more than 80 countries worldwide. Together, numerous companies in the US, Canada, and China have produced more than 8,000,000 rifles of all variants. Approximately 90% are still in operation. The M16 replaced the M14 and M1 carbine as standard infantry rifles of the US armed forces. The M14 continues to see limited service, mostly in sniper, designated marksman, and ceremonial roles. Furure replacement Previous attempts by the US Military to replace the M16 were unsuccessful or only supplemented it. The M4 carbine will eventually replace the M16 rifle in most combat units in the US Army. Background Through the 1970s, the Army experimented with various materials to replace brass in cartridge cases. Brass has a number of qualities that make it almost ideal for a cartridge, including low friction against steel, making it easier to extract, and the ease with which casings can be manufactured. However, brass is also dense and expensive, so replacing it would lower both the cost and weight of the ammunition. Aluminum and steel were popular materials for complete rounds, and AAI successfully developed a plastic blank. Completely caseless ammunition was also studied on several occasions, notably the German 4.7mm designs, and this concept is now being continued with the Lightweight Small Arms Technologies Program. Later in the 1980s, the Advanced Combat Rifle program was run to find a replacement for the M16. Colt entered a modified M16A2 known as the Colt ACR, which used duplex rounds, a system that lowered recoil by 40% to improve repeating shots, and added a 3.5x scope. This weapon, designated M16A2E2, also featured a "guide" of sorts as part of a special handguard developed by the US Army Human Engineering Laboratory designed to assist in snap-shooting, and a carbine style stock very similar to the recent stock developed by the Naval Surface Warfare Center Crane Division. The Steyr ACR used new flechette rounds that was nominally called 5.56mm, with a very high 4,750 ft/s muzzle velocity. Other variants experimented with caseless ammunition technologies as well. In the 1980s, the M249 SAW was issued to infantry units, replacing some M60s and some M16A1s at the squad level. In the 1990s the M4 carbine took over the operational role of the M3 submachine gun, some M9s, and many M16A2s. The US Air Force mostly uses M4 and GUU-5/P carbines for security squadrons and M16A2s for non-security personnel. The USMC has retired the M16A2 in favor of the M16A4 rifle which share almost all the same parts as the A2 but has an optics rail for USMC RCO ACOG scopes. The US Navy has retained the M16A2 and M16A3 for its units that use rifles like the US Navy Seabees. The US Army has largely relegated the M16A2 to non-combat roles, choosing instead the M4 and M4A1. Further, the M16 never entirely replaced the M14 in all roles, which continues to be used in a number of niche applications throughout the Armed Forces, especially with the US Navy. Replacement designs Replacement of the M16 family has been proposed at various points, and its longevity is in part due to a series of failures in projects meant to replace it, driven largely by the requirement for significant improvement. Immediately after the introduction of the M16, the Marine Corps sought to adopt the Stoner 63. Although they found it superior in most ways, it was still at an early stage of development; the Marines chose the technically inferior but mature M16. The Advanced Combat Rifle program in the 1980s produced weapons that were superior in some ways, but none improved upon the M16 series enough to replace it. It was also potentially going to be replaced by the SABR, from the OICW project. The wepaon system originally planned by the OICW project was put on hold around the turn of the century, in favor of a simpler new 5.56mm rifle project that offered less far-reaching improvements. The resulting XM8 rifle was also intended as a potential replacement for the M16 family. However, this program too ran into problems around 2004-05, and was put on hold in favor of an open competition for what became known as the OICW Increment 1. This competition was subsequently put on hold in the summer of 2005 to take into account input from other services; then the competition was cancelled in Oct 2005. A partial replacement for the M16 rifle is the SOF Combat Assault Rifle (SCAR), designated Mk 16. The 5.56x45mm Mk 16 emerged as a winner of a USSOCOM competition to find a new rifle for Special Operations Forces in 2003 and entered operational service in 2009. Most of the SCAR's basic controls share the same location and functino as on the M16 and M4 they are supplementing. Since the cancellation of the XM8 program, and into 2008, the LSAT rifle program has been pursued for the next generation of US small arms. The program has already produced practical results and is currently projected to provide the next US military rifle. Development of the LSAT rifle began in 2008. Several companies have been working on and creating potential candidates for the US Army's next primary weapon. The Heckler & Koch HK416 has been in use by Delta Force since 2004. The HK design replaces the direct impingement gas system with a newer piston design. The HK416 is offered as a conversion kit that can retrofit current M4 carbines. The HK416 recently won a testing competition for the USMC Infantry Automatic Rifle program and entered final testing as the M27 in the summer of 2010. The M27 entered service in 2011, but as a replacement for the M249 SAW, not the M16. The HK416 is also one of several M4 designs on the front competitors of the Army's Individual Carbine competition. The reason to build a new M4 is to produce a new more reliable carbine for US troops in a few years. However, in Nov 2011, leaders of the US Marine Corps announced they will stay with current M4 carbines and M16A4s and not adopt an IC winner. The USMC is considering upgrading the M16A4. Gas piston Complicating the Army search for higher reliability in the M4 is a number of observations of M4 gas piston alternatives that suffer unintended design problems. The first is that many of the gas piston modifications for the M4 isolate the piston so that the piston jams or related malfunction require the entire weapon be disassembled, such disassembly cannot be performed by the end user and requires a qualified armorer to perform out of field, whereas any malfunction with the direct-impingement system can be fixed by the end user in field. The second is that the gas piston alternatives use an off-axis operation of the piston that can introduce carrier tilt, whereby the bolt carrier fails to enter the buffer tube at a straight angle resulting in part wearing. The third is that the use of a sound suppressor results in hot gases entering the chamber, regardless of a direct-gas impingement or gas piston design choice. Category:U.S. Military Category:NATO Weaponry Category:Weapons Category:Western Nations